The present invention relates to a process for producing crosslinked polyolefins. As well as the novel polyolefins produced thereby.
Crosslinking reactions have been widely employed for improving the properties of polyolefins. However, attempts to crosslink .alpha.-olefin polymers such as polypropylene have resulted primarily in degradation reaction of the main rather than the desired crosslinking reaction.
Degradation, and its attendant molecular weight reduction, predominate over crosslinking reaction when radicals are generated by decomposition of peroxides or exposure to radiation. Accordingly, crosslinking has been carried out such that a monomer capable of inducing the crosslinking reaction upon hydrolysis, for example, alkoxyvinylsilane or the like, is initially grafted to the polyolefins, which is thereafter crosslinked. (See for example, Japanese Patent Laid-Open No. 117244/1983).
Polymers obtained by grafting alkoxyvinylsilane to polyolefins are effective to a certain extent for improving physical properties of the polyolefin that result from the subsequent crosslinking. However, processes for the synthesis of graft polymers are complicated and deterioration of the physical properties of the crosslinked polymer due to scission of the main chain remains an inevitable and critical problem of crosslinking reaction.
It is also difficult to introduce various comonomers into the main chain. In this connection, a process has been proposed to introduce vinylsilane into the main chain, and thereafter to crosslink the resultant copolymer with water (See, for example, U.S. Pat. No. 3,223,686).
The crosslinking with water, however, is disadvantageous in that the reaction does not readily processed and thus takes a longer time. A further disadvantage is that articles molded from such polymers to deform upon exposure to high temperatures. A still further a problem with this process is that it involves a relationally complicated operating procedure.
As to the production and application of copolymers of alkenylsilane and olefin, the present inventors have filed Japanese Patent Application Numbers 171020/1988 (corresponding to U.S. application Ser. No. 271,864), 45783/1988 (corresponding to U.S. application Ser. No. 284,680) and 34995/1989. These applications do not disclose radiation treatment of the polymers to effect crosslinking.